The disclosure relates to a bone anchor assembly and method of using the assembly to retain bone portions, such as vertebrae of a spinal column, in a desired spatial relationship. The assembly for retaining vertebrae of a spinal column in a desired spatial relationship may include two or more bone anchors engageable with vertebrae of the spinal column, a longitudinal member extendable along the spinal column, and two or more housings connecting the longitudinal member and the bone anchor.